Traveling wave tubes



Nov. 24, 1959 R. A. PAANANEN 2,914,700

TRAVELING WAVE TUBES 1 Filed Feb. 27. 1958 f VE/VTOQ For 4. @m/vANE/v Arr-02mm TRAVELING WAVE TUBES,

Company, a corporation of Delaware Application February 21, 1953, Serial No. 71 7,897

{I 3 13 Claims. c 31s-s9.3

. This invention concerns atraveling wave tube, and, morey specifically, a modulatedtraveling wave oscillator having means for minimizing the capacitance between the interaction space-bounding electrodes, thereby reducing the modulator powerrequirements.

A traveling wave oscillator of the backward wave type is discussed in a copending application for United States Letters Patentof E. C. Bench and A. D. La Rue, Serial No.: 562,472, filedlanuary 31, 1956, now US. Letters Patent No; 2,888,649, issued May 26, 1959, which includes a lnonreentrant. slow wave energy propagating structure, a continuous electrode or solespaced from and disposed substantially parallel to said structure, and an electron gun mounted to said sole adjacent one end of said structure for producing an electron beam which traverses the interaction space bounded by the slow wave structure andthe sole.- y.

a By.virtue, of the interaction betweengthe electron beam ingin to the interaction space .in the region between the electron gun and the output coupling means. Moreover, attenuation may be provided at the end of the slow wave structure opposite the electron gun for reasons already well known'to those skilled in the traveling wave tube art. The 'portion of the tube including the attenuating means and" the portion adjacent the electron gun, as well as the portion including the collector electrode, if any, may be referred to as the inactive part of the tube, while the remaining portion of the tube may be referred to as the active part of the tube, viz., the part wherein effective exchange of energy between the electron beam and the RF. fields of wave energy alongthe slow wave structure a 'q su t v 1 The velocity of the backward component of a traveling wave ina periodicallyloaded'microwave slow wave structitre, siahas a strapped vane structure or an interdigital line, varies with frequency. As the electron beam velocity is'varied, substantial synchronism may be obtained with the phase velocity of a backward wave component of' the traveling wave, for a given frequency, and oscillations can be generated by the tube. The average velocity of the electron beam is dependent upon the intensity E of'the electric field between the slow wave structure and the sole and also upon the strength B of the transverse magnetic field; the average electron beam velocity is equal to the ratio E/B. .If the spacing at between the anode structure and the sole and the magnetic field strength B are fixedpthe average velocity of the electron (U t /d W 2,914,700 Patented Nov. 24, 1959 beam is dependent only upon the electric field strength B. By varying the strength of the electric field, the beam velocity may be varied, with a resulting variation in frequency of the traveling wave oscillator. If the slow wave structure and sole are supplied by separate sources whose voltages with respect to a common point, such as the cathode, are V and V respectively, the electric field B may be given by:

The electric field may be altered by varying either the positive delay structure voltage V or the negative electrode (sole) voltage V in order to tune the oscillator.

It has been found that a greater tuning range is produced by variation of the voltage V than is possible by variationof the sole voltage V Owing to the comparatively heavy current in the anode delay structure relative to that in the sole, however, the' power requirements for frequency modulation using anode delay structure voltage tuning are greater than those using sole voltage tuning. If only a small amount of tuning is adequate, tuning may be achieved by varying the potential of the sole or negative electrode. This method of tuning is superior to anode delay structure tuning in thatthe current may be of a considerably lower order of magnitude. Such tuning, however, is inadequate for applications in which it is desired to modulate the sole potential at high rates, of the order of say 5 to 10 megacycles, since, as will be explained subsequently, the relatively large negative electrode presents considerable capacitance. The sole electrode preferably is made in the form of an arcuate channel having a major surface'parallel to the delay struc ture and vertical walls or flanges at each edge of the sole which approach or slightly overlap the delay structure. The vertical walls serve as a beam-forming end shield to keep the electron beam centered in the system and from diverging in a direction normal to the path of the electrons as a result of mutual repulsion of the electrons in the space charge existing along the length of the tube.

The major surface of the sole, is spaced relatively close to the delay structure, since' the strength of the electric field produced between the delay structure and the sole is inversely proportional to the radial distance ther'eb'etween. The spacing between the delay structure and the Wall is even smaller in the region of the tips of the vertical walls of the sole. Because of the relatively large size of the sole and its proximity to the anode, the capacitance between the delay line and the sole is quite large. .In addition to the capacitance between the juxtaposed peripheries of the sole and the delay structure there is considerable capacitance betweenthe end faces of the sole and the end portions of the delay structure, which may form a part of the tube envelope; thiscapacitance iscomparatively large because of the relatively large exposed surface areas of the sole and the end portions' of the delay structure. The large capacitance is of no' concern insofar as the unidirectional field-producing means is concerned, but is not permissible for operation at higher frequencies, since the capacitive reactance shunting the modulating voltage source at radio frequencies becomes so low that the power rating of the modulator S necessary to produce ,proper modulation of the electric dividing the sole into two parts, a first of which is substantially coextensive with the inactive section of the delay structure. The second part of the sole, sometimes referred to hereinafter as an auxiliary part, is of greatly reduced volume and total surface area and may, for example, be a thin electrically conductive ring secured to the first part of the sole by electrically insulating supports. The periphery of the second part of the sole forms a continuation of'the first part of the sole, so that the arcuate interaction space between the delay structure and the sole is maintained more or less uniform throughout the length of the tube. A uniform interaction space permits of better operation, since there is no discontinuity in the field existing in the interaction space.

The two parts of the sole must be insulated electrically from one another. Inforder to preserve, as near as possible, a continuous interaction space of uniform width so that the electric field configuration will not be unduly disturbed, and at the same time provide suitable insulation between the two parts, it has been found expedient to taper the ends of the auxiliary part of the sole to a point at the ends, so that the capacitance between the opposed edges of the two parts of the slot is relatively small in spite of a small separation therebetween. The modulating voltage is connected between the auxiliary part of the sole and the anode delay structure.

The depth of. the auxiliary part of the sole need not be as great as that of the more massive portion thereof, since the electron beam in most traveling wave tubes is confined to the central transverse region of the tube; it is in this central region particularly that the more eifective interaction occurs between the electron beam and the radio-frequency fields existing along the anode delay structure. This is particularly true in traveling wave oscillations using interdigital delay structures, since the radio-frequency distribution is a maximum at the center of the tube and a minimum at the side walls. In other words, for purposes of modulating the electric field between the two electrodes, a large negative electrode is not essential. For the same reason, it may be practical in some instances to build the auxiliary part of the sole without the vertical walls or flanges at the edges previously referred to.

Furthermore, the variation in intensity of the electric field required to frequency-modulate the microwave traveling wave oscillator of a comparatively narrow band is relatively small compared with that essential for the main operating frequency. For example, the oscillator may be varied about a minimum frequency of 1500' megacycles at a ten-megacycle rate. The auxiliary part of the sole, therefore, may consist of a more or less centrally located electrode of relatively small surface area and would still be adequate in obtaining the necessary modulation of the electric field.

By reducing the capacity shunted across the RM. modulator, modulation at microwave frequencies may be effected with less driving power and, consequently, with a substantial saving of size and weight of modulating apparatus.

Other and further advantagesof this invention will be apparent as the description thereof proceeds, reference being had to the accompanying drawings, wherein:

Fig. 1 is a cross-sectional View, partly in elevation, of a traveling wave tube taken along the line 11 of Fig. 2, and of a traveling wave oscillatoraccording to the invention;

Fig. 2 is a cross-sectional view of the traveling wave oscillator shown in Fig.- 1;

Fig. 3 is a view illustrating details of the slow wave structure of the tube of Figs. 1 and 2;

Fig. 4 is a view showing details of the sole structure; and

Figs. 5 and 6 are detail views illustrating the electron gun assembly of the oscillator of Figs. 1 and 2.

Referring to the drawing, a traveling wave oscillator 10 is shown which comprises a slow wave energy propagating structure or delay line 12, a cylindrical electrode 14, sometimes referred to as a sole, concentric with said relay line 12 and preferably maintained negative with respect to the slow. wave structure 12, a lead-in assembly 16, an output coupling means 18, an electron gun assembly 20 including at least a cathode 21 and heater 22, and a magnetic field-producing means 25, a portion of which is indicated in Fig. 2.

The circular delay line 12 includes several interdigital fingers or elements 31 and 32 which extend from oppositely disposed annular members 33 and 34, respectively. Members 33 and 34 are secured by screws 35, shown in Fig, 3, to the shoulder portion of a cylindrical' electrically-conductive ring 36. The remainder of the slow wave structure12 includes a pair of oppositely located cover plates 38 and 39 hermetically sealed to ring 36. Although the delay line has been described and illustrated as an interdigital line, the

, invention is not limited thereto; for example, the delay cylindrical segment of an electrically-conductive material, such as'copper, which includes a web portion 45 bounded by an arcuate section 46 whose periphery consistsof a major surface 47 and flanges 48. The purpose of the flanges 48, as mentioned previously, is to confine the electron beam within the interaction space 50 between the surface 47 of sole 14 and the interdigital slow wave structure 12. A tubular metallic insert 52 is brazed into position against the inner periphery of a centrally disposed aperture 53 in the web portion 45 of sole 14. One end of a hollow supporting member 54 is inserted within the insert 52 and is fixedly secured thereto. Supporting member 54, in addition to providing support for the sole 14, forms a portion of lead-in assembly 16 and allows for passage of external circuitconnecting leads, in a manner to be described subsequently. The sole 14 further comprises a portion 55, such as a curved metallic strip, whichmay be mounted from the portion 44 of the sole by electrically insulating posts 57 which may be brazed in position. It

should be understood, however, that any means of mounting portion 55 of the sole to the tube structure may be used, provided that portion 55 is electrically insulated from the slow wave structure 12 and from the portio'n'44 of the sole. Portion 55 of sole 14 is made as thin as possible, that is, the dimension of surface 58 is made as small as possible, consistent with mechanical strength and rigidity, in order to minimize the capacitance between portion 55 of the sole and the end members 38 and 39 of slow wave structure 12, as well as to minimize the capacitance between the portions 55 and 44 of the sole. The periphery of portion 55 of the sole may contain flanges 59, as in the case of the portion 44 of the sole, for reasons already mentioned; however, the flanges 59 are not always necessary and sometimes may be omitted. A modulating input lead 60 is electrically connected to the portion 55 of the sole, as shown in Fig. 4.

The portion 44 of sole 14 contains a slot 62 to accommodate the electron gun assembly 20. Electron gun 20 for the tube of Figs. 1 and- 2 includes a mounting plate 65 containing threaded apertures 66. The mounting plate 65 is attached to the web portion 45 of the sole assembly 14 by means of screw 67 inserted into the apertures 66. Electron gun 20 includes a cathode 21, heater 22, a grid electrode 23, which may be usedfor control of beam current or for amplitude modulating, and an accelerating electrode 24. The cathode 21 maybe in the forrnof a rectangular prism provided witha circular bore 70in which a folded-heater wire 22 is inserted. The heater may be connected at one end to the inner wall of the cathode. The cathode body may be made of porous tungsten and the outer surface coated with an emitter, such as a compound, of barium. A rigid molybdenum cathode supporting lead 71 is spot welded at one end toone end of the cathode body and aflixed at the other end to a metallic terminal 72. Terminal 72 is attached to an insulating mounting post 73, which may be made of ceramic. I The mounting post 73 passes through mountingplate 65-and may be brazed thereto. In this manner, thecathode 21 is mechanically supported in the proper position adjacent to and facing the interaction space 50. An external cathode lead-in wire 74 is attached to metallic terminal 72. One end of the heater 22 ,is connected by a heater supporting lead 75 to 'a m'etallicterminal 76 aifixed to a second insulating mounting post 77, similar in construction to mounting post 73. An external heater lead-in wire 78 is attached to the metallic terminal 76 on mounting post 77. The grid electrode 23 includes a channel-shaped portion 23' surrounding the cathode and an integral flat elongated portion 23" brazed thereto for providing increased heat dissipation from the grid. The portion 23" of the grid contains an opening (not shown), aligned with the cathode 21 to permit emission of the electron beam into the interaction space. Grid 23 is mounted from mounting plate 65 by means of a rigid support wire 79 attached to the portion 2 of the grid and to a terminal 80 fastened to the ceramic post 81; the latter is brazed to the mounting plate 65 in the same manner as mounting posts 73 and 77. i A lead-in wire 82 for the grid is connected I to the. terminal lug 80. The accelerating electrode 24 is positioned adjacent grid 23 and includes a portion disposed directly over the emitting area of the. cathode and an elongated portion substantially parallel to the elongated portion 23" of the grid. The parallel relationship of the grid and accelerating anode serves to maintain a proper electric field therebetween. The accelerating electrode 24, like grid 23, is made relatively large in order to facilitate heat dissipation therefrom. The accelerating electrode 24 is mounted from mounting plate 65 p by meansof a rigid support wire 84 attached to a terminal 85 brazed to insulating post 86 in the mounting plate 65. A lead-in wire 88 for the accelerating electrode 23 is connected to terminal lug 85. V I 1 The various lead-in wires 74, 78, 82, and 88, together with the modulating input lead-in wire 60, are brought out ofthe tube envelope through the tubularsupporting .member 54-of sole 14,. Lead-in assembly 16 includes an. electrically conductive tube 90 affixed to the inner.

periphery of cover plate 38, as shown in Fig. 2. A seetion'of cylindrical glass tubing 91 interconnects electrically conductive tube 90 and a second electrically con-' ductive tube 92. The other end of tube 92 is provided with a glass, seal 93 for sealing the traveling wave tube after evacuation. Tubes 90 and '92 preferably are constructed of a material having an expansion coefficient closely-approximating that of the glass tube 91. The end of sole. supporting member 54 contains an outwardly flared portion 54' which is connected to the inner surspirit and scope of this invention.

ture 12. In some instances, however, the collector electrode may be omitted and the electron stream made reentrant.

The necessary electric field between the slow wave structure 12 and sole 14 may be obtained by means of a unidirectional voltage applied therebetween. The sole 14 may be biased negative with respect to the cathode 21 by means of a source 101 of voltage connected between cathode lead 74 and sole-supporting member 54 by way of tube 92. The cathode 21 may, in some instances, however, be at the same potential as sole 14, in which case source 101 may be omitted. ,Similarly, the delay line 12 may be maintained at a potential positive relative to both sole 14 and cathode 21 by means of a source 103 of unidirectional voltage connected between cathode lead 74 and sleeve 90, the latter being connected,

in turn, to the delay line 12. The accelerating electrode.

24 may be maintained at a positive potential relative to the cathode 21 by means of a source 105 of unidirectional voltage connected between leads 88 and,74. The control grid lead 82 may be connected by way of terminal 107 to an appropriate energy source for controlling the' magnitude of the electron beam current in the traveling wave oscillator 10. The modulation lead 60 is connected to a frequency modulation source 110, shown in Fig. 2. c v

A uniform magnetic field transverse to the direction of propagation of the electron beam'is provided by a permanent magnet, or by an electromagnet, having cylindrical pole pieces 112 and 113 radially positioned on or adjacent the anode cover plates 38 and 39, respectively. Pole piece 112 isapertured to receive the lead-in, assembly 16, includiug the sole-supporting member 54, while pole piece 113 is apertured to maintain symmetry of the magnetic field. The flux lines should be concentrated in the interaction space 50 between sole 14 and delay line 12. By properadjustment of the magnitude and polarity of the magnetic and electric fields, the electron bea-m maybe made to follow a circular path along an interaction space 50 under the combined influence of these transversely disposed fields.

This completes the description of the embodiment of the invention illustrated herein. However, many modifications and advantages thereof will be apparent to persons'skilled in the art without departing from the Accordingly, it is desired that this invention not be limited to the particular details of the embodiment disclosed herein except as defined by the appended claims.

What is claimed is: j

l. A traveling wave oscillating electron discharge device comprising an evacuated envelope within which is disposed an arcuate slow 'wave energy propagating structure producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, a cylin- 1 drical enclosure forming a portion of said envelope, said envelope further including closure members disposed at corresponding ends of said enclosure, an electrode assembly spaced from and substantially juxtaposed with said slow wave structure, and means. for directing electrons along said region in energy-exchanging relation with said face of tube 92. The lea ds 60, 74, 78, 82, and 88 are insulatedlysupported from the supporting member 54 by one or more glass beads 95. I p The coaxial output coupling means 18 is sealed in an opening of wall 36 of the delay line 12 and isimpedancematched to the delay line." The inner conductor 96 of the output coupling means 18 is connected to a finger of the delay line 12 at or near the end of the delay line adjacen t the electron gun 20.

Traveling wave tube 10 may be provided with a collectorelectrode 98, shown in Fig. 1, for intercepting electrons afterone traversal of the arcuate interaction space 50. This collector electrode may take the form of a'projection from the backwall 36 of the delay strucsurface to said slow wave structure which is substantially fields of wave energy, said electrode assembly including a first portion and a second portion, the surface area of the surface of said second portion facing the adjacent closure member being substantially smaller than the surface area of the surface of the first portion facing said corresponding closure member, the second portion of said electrode assembly being electrically isolated from said first portion, said first and second portions of said electrode assembly presenting a substantially continuous uniformly spaced from said structure.

2. A traveling wave oscillating electron discharge device comprising an evacuated envelope within which is disposed an arcuate slowwaveenergy propagating structure which is g of substantially uniform construction throughout and producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, a cylindrical enclosure forming a portion of said envelope, said envelope further including closure members disposed at corresponding ends of said enclosure, an electrode assembly spaced from and substantially juxtaposed with said slow wave structure, and means for directing electrons along said region in energy-exchanging relation with said fields of wave energy, said electrode assembly including a first portion and a second portion, the surface area of the surface of said second portion facing the adjacent-closure member being substantially smaller than the surface area of the surface of the first portion facing said corresponding closure member, said first and second portions of said electrode assembly presenting a substantially continuous surface to said slow wave structure which is substantially uniformly spaced from said structure.

' 3. A traveling wave oscillating electron discharge device comprising an evacuated envelope within which is disposed an areuate slow Wave energy propagating structure which is of substantially uniform construction throughout and producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, a cylindrical enclosure forming a portion of said envelope, said envelope further including closure members disposed at corresponding ends of said enclosure, an electrode assembly spaced from and substantially juxtaposed with said slow Wave structure, and means for directing electrons along said region in energy-exchanging relation with said fields of wave energy, said electrode assembly including a first portion and a second portion, the radial thickness of said second portion of said electrode assembly being substantially smaller than that of said first portion.

4. A traveling wave electron discharge device comprising a slow wave energy propagating structurewhich is of substantially uniform construction throughout and producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, an electrode assembly spaced from and substantially juxtaposed with said slow wave structure, and means for directing electrons along said region in energy-exchanging relation with said fields of Wave energy, said electrode assembly including a first portion and a second portion, the second portion of said electrode assembly being electrically isolated from said first portion, said first and second portions of said electrode assembly presenting a substantially continuous surface to said slow wavestructure, the radial thickness of said second portion being substantially smaller than that of said first portion.

A traveling wave electron discharge device comprising an evacuated envelope within which is disposed an arcuateslow wave energy propagating structure which is of substantially uniform construction throughout and producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, a cylindrical enclosure forming a portion of said envelope, said envelope further including closure members disposed at corresponding ends of said enclosure, an electrode assembly spaced from and substantially juxtaposed with said slow wave structure, and means for directing electrons along said regionin energy-exchanging relation with said fields of wave energy, said electrode assembly including-a first portion and a second portion, said second portion forming with said corresponding closure member a capacitor whose capacitance is small compared with that of the capacitance between said first portion and said corresponding closure member, the second portion of said electrode assembly further being electrically isolated from said first portion.

6. A traveling wave oscillating electron discharge device comprising an evacuated envelope within which is disposed an arcuate slow wave energy propagating structure which i's of substantially uniform construction throughout and producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, a cylindrical enclosure forming a portion of said envelope, said envelope further including closure members disposed at corresponding ends of said enclosure, an electrode assembly spaced from and substantially juxtaposed with said slow Wave structure, means for directing electrons along said region in energy-exchanging relation with said fields of wave energy, said electrode assembly including a first portion and a second portion, the surface area of the surface of said second portion facing the adjacent closure member being substantially smaller than the surface area of the surface of the first portion facing said corresponding closure member, the second portion of said electrode assembly being electrically isolated from said first portion, and means for supplying a modulating potential between said structure and said second portion only of said electrode assembly for varying the frequency of oscillation of said device.

7. A traveling wave oscillating electron discharge device comprising a slow wave energy propagating structure producing in the region adjacent thereto fields of electromagnetic Wave energy being propagated, an electrode assembly spaced from and substantially coextensive with said slow wave structure, means for directing electrons along said region in energy-exchanging relation with said fields of wave energy, said electrode assembly including a first portion and a second portion, the second portion of said electrode assembly being electrically isolated from said first portion, said means for directing including means for supplying a unidirectional voltage between said struc ture and said electrode assembly for establishing an electric field therebetwee'n whose strength is dependent upon the magnitude of said voltage, the frequency of oscillation produced in said device being a function of the strength of said electric field, said first and second portions of said electrode assembly presenting a substantially continuous surface to said slow wave structure, said second portion of said electrode assembly having substantially smaller surface areathan said first portion, and means for supplying a modulating potential between said structure and said second portion only of said electrode assembly for modifying the strength of said electric field as a function of said modulating potential to modulate the frequency of said device.

8. A traveling wave oscillating electron discharge device comprising a slow wave energy propagating structure which is of substantially uniform construction throughout and producing'in the region adjacent thereto fields of electromagnetic wave energy being propagated, and means including an electron source positioned adjacent said structure and an electrode assembly spaced from and coextensive with said sloW wave structure for directing electrons along said region in energy-exchanging relation with said fields of Wave energy, said means for directing including means for producing a unidirectional voltage between said structure and said electrode assembly, said electrode assembly including a first portion and a second portion, the radial thickness of said second portion of said electrode assembly being substantially smaller than that of said first portion, and means for supplying a modulating potential between said structure and said second portion only of said electrode assembly for effecting frequency modulation of said device as a function of said unidirectional voltage.

9. A traveling wave oscillating electron discharge device comprising a slow wave energy propagating structure which is of substantially uniform construction throughout and producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, and means including an electron source positioned adjacent said structure and an electrode assembly spaced from and coextensive with said slow Wave structure for directing electrons along said region in energyexchanging relation with said fields of wave energy, said means for directing including means for producing a magall;

,9 netic field transverse to said region,'said electrode assembly including a first portion and a second portion, the second portion of said electrode assembly being electrically isolated from said first portion, the radial thickness of said second portion of said electrode assembly being substantially smaller than that of said first portion, and means for supplying a modulating potential between said structure and said second portion only of said electrode assembly for effecting frequency modulation of said device.

10. A traveling wave oscillating electron discharge device comprising a slow Wave energy propagating structure which is of substantially uniform construction throughout and producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, means including an electron source positioned adjacent said structure and an electrode assembly spaced from and coextensive with said slow wave structure for directing electrons along said region in energy-exchanging relation with said fields of wave energy, said electrode assembly including a first portion and a second portion, said electron source being carried by the first portion of said assembly, the second portion of said electrode assembly being electrically isolated from said first portion, said second portion of said electrode assembly having substantially smaller volume and surface area than said first portion, the radial dimension of said second portion being substantially less than that of said portion, and means for supplying a modulating potential between said structure and said second portion only of said electrode assembly for modulating the frequency ofoscillation of said device.

11. A traveling wave oscillating electron discharge device comprising a slow wave energy propagating structure which is of substantially uniform construction throughout and producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, said device including an active section and an inactive section, an electrode assembly including a first portion spaced from and substantially coextensive with said active section of said device and a second portion spaced from and coextensive with said inactive section of said device, and means for directing electrons along paths adjacent said slow wave structure in energy-exchanging relation with said fields of wave energy.

' 12; A traveling wave oscillating electron discharge device comprising a slow wave energy propagating structure which is of substantially uniform construction throughout electromagnetic wave energy being propagated, said device including an active section and an inactive section, an electrode assembly including a first portion spaced from and substantially coextensive with said active section of said device and a second portion spaced from and coextensive with said inactive section of said device, and means for directing electrons along paths adjacent said slow wave structure in energy-exchanging relation with said fields of wave energy, the second portion of said electrode assembly being electrically isolated from said first portion. 7

13. A traveling wave electron discharge device comprising a slow wave energy propagating structure producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, said device including an active section and an inactive section, an electrode assembly including a first portion spaced from and substantially coextensive with said active section of said device and a second portion spaced from and coextensive with said inactive section of said device, and means for directing electrons alongpaths adjacent said slow wave structure in energy-exchanging relation with said fields of wave energy, said first'and second portions of said electrode assembly presenting a substantially continuous surface to said slow wave structure, the ends of said second portion of said assembly adjacent said first portion'being tapered to reduce the capacitance between said first and second portions.

14. A traveling wave electron discharge devicecomprising a slow wave energy propagating structure producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, said device including an active section and an inactive section, an electrode assembly including a first portion spaced from and substantially coextensive with said active section of said device and a second portion spaced from and coextensive with said inactive section of said device, and means for directing electrons along paths adjacent said slow wave structure in energy-exchanging relation with said fields of wave energy, said second portion of said electrode assembly having substantially smaller surface area than said first portion.

15. A traveling Wave oscillating electron discharge device comprising a slow wave energy propagating structure producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, said device including an active section and an inactive section, an electrode assembly including a first portion spaced from and substantially coextensive with said active section of said device and a second portion spaced from and coextensive with said inactive section of said device, means for directture in energy-exchanging relation With said fields of Wave energy, and means for supplying a modulating pop and producing in the region adjacent thereto fields of I tential between said structure and said second portion only of said electrode assembly for modulating the frequency of oscillation of said device.

16. A traveling Wave oscillating electron discharge device comprising a slow wave energy propagating structure producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, said device including an active section and an inactive section, an electrode assembly including a first portion spaced from and substantially coextensive with said active section of said device and a second portion spaced from and coextensive with said inactive section of said device, and means for directing electrons along paths adjacent said slow wave structure in energy-exchanging relation with said fields of wave energy, the second portion of said electrode assembly being electrically isolated from said first portion, said second portion of said electrode assembly having substantially smaller surface area and a smaller radial thickness than said first portion.

17. A traveling wave oscillating electron discharge device comprising a slow wave energy propagating structure producing in the region adjacent thereto fields of electromagnetic Wave energy being propagated, said device including an active section and an inactive section, an electrode assembly including a first portion spaced from and substantially coextensive with said active section of said device and a second portion spaced from and coextensive with said inactive section of said device, means for directing electrons along paths adjacent said slow wave structure in energy-exchanging relation with said fields of Wave energy, the second portion of said electrode assembly being electrically isolated from said first portion, said second portion of said electrode assembly having substantially smaller surface area than said first portion, and means for supplying a modulating potential between said structure and said second portion only of said electrode assembly for modulating the frequency of oscillation of said device.

18. A traveling wave electron discharge device comprising a slow wave energy propagating structure producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, an electrode assembly spaced from and substantially coextensive with said slow wave structure, means for directing electrons along said region in energy-exchanging relation with said fields of wave energy, said electrode assembly including a first portion and a second portion, the second portion of said electrode assembly being electrically isolated from said 1T 12 first portion, said first and second portions of said elecsecond portion only of said electrode assembly for modutrode assembly presenting a substantially continuous surlating the frequency of said device. face to said slow wave structure, said second portion of said electrode assembly having substantially smaller surh fi d f 1 References Cited in the file of this patent face area t an said rst portion, an means or supp ying 5 a modulating potential between said structure and said UNITED STATES PATENTS 2,794,936 Huber June 4, 1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIN Patent No. 2,914,700 November 24, 1959 Roy A. Paananen It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 5, for "relay" read delay column 9, line 28, after "said" insert first column 10, l ne 25, after "directinsert ing electrons along paths ad acent said slow wave struc- Signed and sealed this 21st day of June 1960.,

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting ()ificer Commissioner of Patents 

